Lens



Dec. 1924. 1,520,617

E. D. TILLYER ET AL- Filed April 1'7, 1922 F/ZTYE Patented Dec. 23, 1924.

UNITED STATES EDGAR D. TIILYER AND ANNA ESTELLE GLANCY, OF SOUTHIBRIDGE, MASSACH'EL PATENT OFFiCE.

SETTS, ASSIGNOBS TO AMERICAN OPTICAL COMPANY, OF SOUTHIBRIDGE, MASSA- CHUSETTS, A VOLUNTARY ASSOCIATION OF MASSACHUSETTS.

LENS.

Application filed April 17, 1922. Serial No. 553,574.

To all whom it may concern:

Be it known that we, EDGAR D. TILLYER and ANNA E. GLANoY, citizens of the United States, residing at Southbridge, in

5 the county of Worcester and State of Massachusetts have invented certain new and useful Improvements in Lenses, of which the following is a specification.

This invention relates to a new and useful bifocal lens and a process in the forming of two part lenses well known in the art as Kryptok lenses. It is a well known fact that in a finished lens of this type, the oblique vision thru the reading portion of the lens has an optical astigmatism which is quite pronounced and objectionable.

One of the main objects of our invention is to provide an improved bifocal lens formed of two pieces of glass and which will 0 be practically free from the objectionable astigmatism present in the reading portion of prior art lenses of this type. Another object of our invention is to introduce a new and improved process for formin two part 5 lenses whereby to eliminate the ob ectionable astigmatism whereby to pro'ducea reasonably correct oblique vision or visions thru the reading portion of the lens.

Another object of our invention is the provision of a process which is included in the making of two part lenses wherein the countersink of one of the parts which receives the other part of the lens, is ground in .toric form that is, different curvatures ini the two major meridians whereby to neutralize the astigmatism introduced and thus provide a finished lens having a. substantially correct. vision thru the reading portion.

a With .the above and other objects in view the. invention consists in the novel features of construction, the combination and arrangement of parts hereinafter more fully set forth, pointed out in the claims and i shown in the accompanying drawings, in

which i Figure I represents a plan. view of a two part lens.

Figure II is a side elevation showing the P countersink near the lower edge of the, lens. Figure III is a side view illustrating the pountersink in the central portion of the ens.

Figure IV is a prospective view of 'a countersink.

decrease in the distortion and the advantages gained with our improved process.

Referring more particularly to the drawings in which we have illustrated our improved lens and processtogether with the advantages gained over the lenses in use at the present time, the numeral 1 indicates the body blank of our improved lens having a countersink'2. into which the button 3 is fitted and then heated to a melting point so that the button will readily conform to the shape of. the countersink and adhere thereto. The roughened surface of the lens is then ground ofl leaving a polished .two part lens. I

In the construction of lenses. of this type it has been found that optical astigmatism is present in the marginal portion of what is known as the reading part produced by the combination ofthe button 3 and the countersink 2, or in other wordsthe power in the marginal portion of .the reading portion is difi'erent from the truepower. at the axial reduce the astigmatism in this portion of the lens to a minimum andin order to, overcome this astigmatism we have added to the process the grinding of, atoric curve'in the portion of the reading portion, adefect usual in all types of lenses. It is, therefore, one ofthe main objects of our process to countersink 2 to neutralize the astigmatism introduced, instead 5 of the. usual spherical Attention is calledf to, fact that in some cases it will be necessary to grind the countersink with the strong-acu rve of the ,toric on a horizontal meridianaand in anescape, thus preventing bubbles, etc.

focus or power in the marginal portions of the reading portion as well as astigmatic errors and our invention will reduce the focal errors as well as the astigmatic ones.

In generalfa lens gives the true required power only along the optic axis. The periph:

eral portion of a lens does not image the object at the same focal point as the center of the lens. For instance, in the case of oblique vision through the reading portion of a fused bifocal we are concerned with two aberrations, (besides the chromatic) namely, an error in the power and a cylinder action or astigmatism. In other words, if the object is a wire mesh having rectangular lines, the best possible image is at a different distance from the lens than it would be if seen along the optic axis, and furthermore, if one set of lines is made sharp the other set of lines is out of focus. 7

For a given lens the amount of these two aberrations; (1) error in power, (2) ast1gmatism, can be calculated by standard text book formulae for any chosen point; for 111- stance, point five-millimeters below the dividing line. Since the countersink surface is concerned only with the reading portion we have at hand a means of correcting the reading errors without altering the distance portion. Hence the countersink curve, winch has always been made spherical heretofore, can be made toric to compensate for the errors of oblique vision. The axis of the toric may be in any orientation, depending upon the prescription, but for a spherical prescription it will be either horizontal or vertical.

Itis to benoticed-that the countersink being of crown glass, fusion does not alter the curves, whereas if the flint button were made toric fusion would destroy the toric character of the'button. A toric utton cannot be substituted for a toric countersink.

In the process of forming a lens of this character attention is called to the fact that the button 3 is a spherical button fitted into a toric countersink 2 while the prior art has disclosed a spherical countersink With a toric button for a different purpose. With our improved combination, as shown in Figure VI, the necessity of wedges and other means for blocking the button to position the same within the countersink for heating can be eliminated, as the button will rest within the countersink in the position illustrated in Figure VI so that when the button is heated to a melting point the edges of the button will drop downwardly and conform to the shape of the countersink, allowing the air to From the above it will be readily apparent that by grinding the countersink 2 in a toric form and by having the spherical button to be fitted within the countersink in the proper axial relationship it will neutralize the astigmatism introduced, thus giving a reasonably correctioblique vision or visions thru the reading p'ortion which is always oblique. Itwill belnoted that by grinding a toric in the countersink on the roperline in accordance with the position of the astigmatism present in the lens it will provide a lens of less distortion and with more accurate power than with the present process of grinding and forming these two part lenses.

VS e are well aware of the fact that lenses of this nature have been constructed heretofore with a toric button anda spherical countersink but fully believe that the process of constructing lenses as set forth above is entirely new in the art.

We claim lfA two part bifocal lens comprising a major blank having a toric countersink formed therein and a segment of different refractiveindex secured within and filling the countersink, for the purpose-set forth.

2. A two part bifocal lens com rising a major blank having a countersin formed therein having a difference in curvature in the two major meridians and a segment of different refractive index secured Within the countersink, for the purpose set forth.

3. A two part bifocal lens comprising a major blank having a curved countersink formed therein to produce a reading portion of spherical power, said countersink being of unequal curvature in'the two major meridians, the curvatures being positioned to counteract and neutralize oblique errors present in the marginal portion of a spherical countersink, and a segment of different refractive index secured in the countersink.

4. A bifocal lens having major vision field and a laterally displaced minor vision field determined by curved surfaces having a known focal effect in' combination, one at least of said curved surfaces departing from true spherical form inversely of the departure from true focal effect produced by oblique vision through the laterally disp aced vision field to maintain the desired focal effect in said field.

5. A two part bifocal lens comprising a major blank having a curved countersink formed therein to produce a reading portion of spherical power, said countersink being of unequal curvature in the two major meridians, the curvatures being positioned to counteract and neutralize oblique errors ofastigmatism present in the marginal portion of a spherical countersink, and a segment of different refractive index secured in the countersink.

EDGAR D. TILLYER. A. ESTELLE GLANGY. 

